1. Field of the Invention
The present invention relates to an electronic component in which a functional element, such as a SAW filter element, BAW filter element, MEMS element, or switch IC, is disposed on a first principal surface of an element substrate, a method of manufacturing the same, a composite module including an electronic component, and a method of manufacturing the same.
2. Description of the Related Art
Electronic components in which functional elements, such as surface acoustic wave (SAW) filter elements, bulk acoustic wave (BAW) filter elements, micro-electro-mechanical systems (MEMS) elements, and switch ICs, are disposed on first principal surfaces of element substrates have become popular in recent years. In one such electronic component, each functional element is confined in a predetermined hermetically sealed space to enable a SAW filter element using a surface acoustic wave of an element substrate made of a piezoelectric material or a BAW filter element using a bulk acoustic wave, which is resonance vibration of a piezoelectric film itself, to be properly excited and to enable an MEMS element or switch IC having a mechanical operating portion to normally operate. Confining each functional element in the predetermined hermetically sealed space can prevent degradation in the characteristics of each functional element.
For example, in an electronic component 500 illustrated in FIG. 10 as one known example, a comb-shaped electrode 502 is formed on a first principal surface of an element substrate 501 made of a piezoelectric material, and thus a functional element made of a SAW filter element is disposed. The element substrate 501 is arranged such that the SAW filter element on the first principal surface faces a base substrate 506 (see, for example, Japanese Unexamined Patent Application Publication No. 2003-158436). Connection electrodes including terminal electrodes 503 electrically coupled to the comb-shaped electrode 502 and metal bumps 504 and an insulating layer 505 surrounding the SAW filter element and the connection electrodes are disposed on the first principal surface of the element substrate 501.
Connection terminals 507 are disposed on a mounting surface of the base substrate 506, and mounting electrodes 508 for use in external connection are disposed on its opposite surface. The connection terminals 507 and the mounting electrodes 508 are electrically coupled to each other with via conductors 509. The metal bumps 504 on the element substrate 501 are connected to the connection terminals 507 on the base substrate 506, the element substrate 501 is mounted on the base substrate 506, and thus a hermetically sealed space surrounded by the insulating layer 505 is formed between the element substrate 501 and the base substrate 506. The SAW filter element is confined in that hermetically sealed space.
The mounting surface of the base substrate 506 is filled with molding resin, and the element substrate 501 is molded and protected by a molding layer 510. Because the above-described configuration enables the comb-shaped electrode 502 (piezoelectric material) arranged in the hermetically sealed space to be properly excited, a surface acoustic wave produced by an input of a signal can normally travel along the surface of the element substrate 501, and degradation in the comb-shaped electrode 502 arranged in the hermetically sealed space can be avoided.
Miniaturization in mobile communication terminals has rapidly advanced in recent years, and there has been a need for further reducing the height and size of composite modules incorporated in the mobile communication terminals. Accordingly, with the aim of reducing the height and size of the above-described electronic component incorporated in each of the composite modules, the electronic component having a bare chip mounting structure is provided. In the electronic component having the bare chip mounting structure, an insulating layer that surrounds a predetermined area in a first principal surface of an element substrate on which a functional element is disposed is laminated with a cover layer. The functional element is confined in a space that is surrounded by the insulating layer and that is formed between the element substrate and the cover layer.
An electronic component having a wafer level-chip size package (WL-CSP) structure can have a configuration in which a cover layer is removed to further reduce its height and size. In that case, however, because a connection electrode disposed on a first principal surface of an element substrate included in the electronic component and electrically coupled to a functional element is in an exposed state, after the electronic component is manufactured, the connection electrode may separate, for example, in the course of moving the electronic component.